Project Summary/Abstract Research: Acute myeloid leukemia (AML) has a high relapse rate and is very difficult to cure, in large part due to the persistence of quiescent, chemotherapy-resistant leukemia stem cells (LSCs). Successful eradication of LSCs would greatly improve AML cure rates, but specific targeting of LSCs has been difficult to achieve because LSCs are rare and difficult to study. This proposal builds on my novel preliminary data indicating that the Rac-GAP Arhgap25 is required for leukemic transformation of HSCs. To understand more fully the requirement for and mechanisms underpinning the role of Arhgap25 AML leukemogenesis, I propose three distinct and complementary lines of investigation in this application, all of which target LSC survival and maintenance. First, I will fully characterize the cell-of-origin-specific nature of the requirement for Arhgap25 in leukemogenesis in multiple models of AML. Second, I will identify the phosphorylation events that permit or prohibit the ability of Arhgap25 to contribute to leukemogenesis. Finally, I will dissect the biochemical mechanisms responsible for Arhgap25 requirement in the maintenance and survival of AML LSCs. These studies will lay the groundwork for developing clinically useful combination therapies for AML and, ultimately, improving AML cure rates. Environment: The Dana-Farber Cancer Institute (DFCI), Boston Children?s Hospital (BCH), and the Joslin Diabetes Center at Harvard University are internationally recognized research programs with a number of world-renowned researchers in the areas of stem cell biology, hematopoiesis, and cancer biology. The Division of Pediatric Hematology/Oncology/Stem Cell Transplantation at the Dana-Farber/Boston Children?s Cancer and Blood Disorders Center, in particular, has a long and distinguished record of training successful physician-scientists. I have assembled an excellent mentoring and advisory committee, consisting of Dr. Amy Wagers, Dr. David Williams, Dr. Leonard Zon, Dr. Kimberly Stegmaier, and Dr. Yi Zheng, who will guide me through my research and training experiences. Dr. Zheng, who has joined my advisory committee for this resubmission, is one of the world?s experts in small GTPase biochemistry, and will aid significantly in providing essential additional training in Rac biochemical techniques and strategies. Candidate Career Goals: My long-term career objective is to compete successfully for R01 funding as a tenure-track, independent physician-scientist in a pediatric hematology/oncology/stem cell transplantation department. A K08 award will provide the senior mentorship and expertise needed to advance my training, develop my proficiency in new techniques, and develop my mastery of new concepts. It will also provide critically important protected time so that I can develop my ideas and projects and bring them to publication in support of further NIH grant submissions. This research proposal is part of a structured plan with scientific, technical, clinical, and career developmental components. The research will be performed under the guidance of Dr. Amy Wagers at the Joslin Diabetes Center and Harvard Stem Cell Institute and Dr. David Williams at the Boston Children?s Hospital and Dana-Farber Cancer Institute. The career development plan builds upon my prior research and clinical experiences with the goal of ensuring that I acquire the expertise required to become a successful, independent investigator with a focus on translational leukemia stem cell therapeutics.